High Recovery Desalination and Mineral Production System and Method

Abstract

A system and method for increasing the water production efficiency of a desalination plant and producing concentrated calcium and magnesium is provided. A saline source water is preferably subjected to a first treatment such a passage through a first desalination unit, followed by dual treatment of the first treatment reject stream using physicochemical adsorption and electrodialysis to remove scale-forming calcium and magnesium. The reject stream from the dual treatment may then be received by a second desalination unit. Due to the removal of the majority of the saline source water's scale-forming minerals, the second desalination unit may be operated at higher operating limits than in conventional desalination units without significant concern for fouling due to scaling. The approach of the present system and method efficiently increases the fresh water production ratio from the source saline water while generating commercially attractive concentrated calcium and magnesium products.

What is claimed is: 
     
         1 . A desalination system, comprising:
 a first desalination unit configured to receive saline water and produce a first desalinated product water stream and a reject stream from the saline water;   a calcium adsorbent unit configured to remove calcium from the first desalination reject stream;   an electrodialysis unit configured to remove magnesium from the first desalination reject stream; and   a second desalination unit configured to receive the first desalination reject stream after removal of calcium by the calcium adsorbent unit and magnesium by the electrodialysis unit and produce a second desalinated product water stream and a second desalination unit reject stream.   
     
     
         2 . The desalination system of  claim 1 , wherein
 the second desalination unit is operated with a concentration factor of 1.5.   
     
     
         3 . The desalination system of  claim 2 , wherein
 the calcium adsorbent unit includes calcium-capturing zeolite material.   
     
     
         4 . The desalination system of  claim 3 , wherein
 the calcium-capturing zeolite material is contained in at least two vessels, and   the at least two vessels are isolatable from one another in a manner that permits calcium recovery back-flushing in at least one of the at least two vessels while the first desalination reject stream continues to be received by another one of the at least two vessels.   
     
     
         5 . The desalination system of  claim 4 , wherein
 the calcium absorbent unit receives the first desalination reject stream from the first desalination unit and outputs the first desalination reject stream with reduced calcium concentration to the electrodialysis unit, and   the electrodialysis unit outputs the first desalination reject stream with the reduced calcium concentration and the reduced magnesium concentration to the second desalination unit.   
     
     
         6 . The desalination system of  claim 4 , wherein
 the electrodialysis unit receives the first desalination reject stream from the first desalination unit and outputs the first desalination reject stream with reduced magnesium concentration to the calcium absorbent unit, and   the calcium adsorbent unit outputs the first desalination reject stream with the reduced calcium concentration and the reduced magnesium concentration to the second desalination unit.   
     
     
         7 . The desalination system of  claim 5 , wherein at least a portion of a second desalination unit reject stream is recycled to the calcium adsorbent unit. 
     
     
         8 . The desalination system of  claim 5 , wherein at least a portion of a second desalination unit reject stream is recycled to the calcium adsorbent unit. 
     
     
         9 . The desalination system of  claim 1 , wherein
 at least a portion of the second desalination unit reject stream is output to at least one of a solar pond and a desalination plant zero liquid discharge system.   
     
     
         10 . The desalination system of  claim 9 , wherein
 the zero liquid discharge system includes crystallization by at least one of a thermal and a reverse osmosis process.   
     
     
         11 . The desalination system of  claim 1 , wherein
 the calcium adsorbent unit and the electrodialysis unit cooperate to remove from the first desalination reject stream at least 90% of calcium and magnesium in the saline water.   
     
     
         12 . A method of operating a desalination unit, comprising the acts of:
 selectively filtering water using a dual treatment system to remove calcium and magnesium from the water, the dual treatment system including a physicochemical adsorption unit configured to remove calcium and an electrodialysis unit configured to remove magnesium;   directing a reject stream from the dual treatment system to a downstream desalination unit; and   producing using the downstream desalination unit a product water stream and a concentrated salt reject stream.   
     
     
         13 . The method of  claim 12 , further comprising the act of:
 before the selective filtering act, desalinating saline water to produce the water to be selectively filtered using the dual treatment system.   
     
     
         14 . The method of  claim 13 , wherein
 in the dual treatment system, the physicochemical adsorption unit is upstream of the electrodialysis unit.   
     
     
         15 . The method of  claim 13 , wherein
 in the dual treatment system, the electrodialysis unit physicochemical adsorption unit is upstream of the physicochemical adsorption unit.   
     
     
         16 . The method of  claim 13 , further comprising the act of:
 directing at least a portion of a second desalination unit reject stream to at least one of a solar pond and a desalination plant zero liquid discharge system.   
     
     
         17 . The method of  claim 12 , wherein
 the dual treatment system removes at least 90% of the calcium and the magnesium in the saline water.   
     
     
         18 . The method of  claim 13 , further comprising the acts of:
 directing at least a portion of a second desalination unit reject stream to a desalination plant zero liquid discharge system; and   performing crystallization in the desalination plant zero liquid discharge system by a thermal process or a reverse osmosis process.   
     
     
         19 . The method of  claim 12 , wherein
 the physicochemical adsorption unit includes at least two vessels containing a calcium-capturing zeolite material, and   the at least two vessels are isolatable from one another in a manner that permits calcium recovery back-flushing in at least one of the at least two vessels while the first desalination reject stream continues to be received by another one of the at least two vessels.   
     
     
         20 . The method of  claim 19 , further comprising the act of:
 recovering calcium from at least one of the vessels by back-flushing.